The present invention relates to a method of forming quantum dots for quantum effect device.
Quantum dots are regions which are sized to shut in electrons of electron quantum mechanical type waves having a wave length in the order of 10 nm. Currently, there is widespread research into devices which include individual quantum dots which are fabricated in semiconductive materials using laser beams and photolithographic technology.
The next generation of such devices however, will not limited to the use of individual quantum dots and will include a plurality of closely grouped dots. Among these new devices which are under investigation are those which use the so called tunnel phenomenon which occurs between this kind of closely grouped quantum dots.
In order to fabricate devices which include lines of closely arranged quantum dots it has been thought to use electron beams and photolithography. In this connection, a work piece has been coated with an organic photoresist which is subject to reaction by an electron bean. This photo resist is patterned via irradiation with a finely focussed electron beam, and the patterning used as a mask for etching via which microscopic fabrication operations are carried out.
However, with this method, the electrons from the irradiated electron beam, scatter within the resist layer which is coated on the work piece, and react therewith. This phenomenon is referred to as a proximity effect.
When using the above type of method, due to the proximity effect, the proximity with which a group of quantum dots can be formed is limited to about 50 nm, and this prevents the desired tunnel effect from being obtained.
An alternate method of forming quantum dots which also uses an electron beam but which is not limited to the previously mentioned resist coating, is such that the resist can be applied by supplying the materials from which the resist is formed, in gaseous form and irradiating the surface of the work piece with the finely focussed electron beam. An example of such a method is disclosed in U.S. Pat. No. 5,171,718 filed in the name of Ishibashi et al.
With the just mentioned type of technology it is possible to achieve a 10 nm degree precision, and as the above mentioned proximity effect is absent, it is possible to form quantum dots in the required proximity of one another.
However, scanning near the peripheral sections of the areas is very difficult and the production of quantum dots on a large scale cannot be improved. Further, as only one electron beam is available for scanning, the formation efficiency of a plurality of quantum dots on a large scale, is poor and an extremely long scanning time is required for the production.